A Distant Glimpse of Uranus

JPL PIA17178 (detail)Last month, Cassini got its first-ever glimpse of Uranus:

NASA’s Cassini spacecraft has captured its first-ever image of the pale blue ice-giant planet Uranus in the distance beyond Saturn’s rings.

The planets Uranus and Neptune are sometimes referred to as “ice giants” to distinguish them from their larger siblings, Jupiter and Saturn, the classic “gas giants.” The moniker derives from the fact that a comparatively large part of the planets’ composition consists of water, ammonia and methane, which are typically frozen as ices in the cold depths of the outer solar system. Jupiter and Saturn are made almost entirely of hydrogen and helium, with smaller percentages of these ices.

When this view was obtained, Uranus was nearly on the opposite side of the sun as seen from Saturn, at a distance of approximately 28.6 astronomical units from Cassini and Saturn. An astronomical unit is the average distance from Earth to the sun, equal to 93 million miles (150 million kilometers). At their closest, the two planets approach to within about 10 astronomical units of each other.

Just to be clear, all those AUs add up to just under 4.3 billion kilometers (2.66b miles).

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Dyches, Preston and Steve Mullns. “Cassini Spies the Ice-Giant Planet Uranus”. Jet Propulsion Laboratory. May 1, 2014.

NASA/JPL-Caltech/Space Science Institute. “PIA17178: Blue Orb on the Horizon”. Photojournal. May 1, 2014.

Cassini: Cosmic Gestation?

File under, And we are so amazed ….

JPL explains:

Say hello to Peggy.NASA’s Cassini spacecraft has documented the formation of a small icy object within the rings of Saturn that may be a new moon, and may also provide clues to the formation of the planet’s known moons.

Images taken with Cassini’s narrow angle camera on April 15, 2013, show disturbances at the very edge of Saturn’s A ring — the outermost of the planet’s large, bright rings. One of these disturbances is an arc about 20 percent brighter than its surroundings, 750 miles (1,200 kilometers) long and 6 miles (10 kilometers) wide. Scientists also found unusual protuberances in the usually smooth profile at the ring’s edge. Scientists believe the arc and protuberances are caused by the gravitational effects of a nearby object. Details of the observations were published online today (April 14, 2014) by the journal Icarus.

Yes, you read that correctly.

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Look Ahead: Cassini “Proximal” Mission

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First, there was Equinox. And then came Solstice. Ever faithful, the Cassini probe continues to defy even the wildest expectations at its launch in 1997. And now, NASA is asking for public participation in preparing the spacecraft for its final mission:

Starting in late 2016, the Cassini spacecraft will repeatedly climb high above Saturn’s north pole, flying just outside its narrow F ring. Cassini will probe the water-rich plume of the active geysers on the planet’s intriguing moon Enceladus, and then will hop the rings and dive between the planet and innermost ring 22 times.

JPL-CassiniProximalMission-1Because the spacecraft will be very close to Saturn, the team has been calling this phase “the proximal orbits.” But they think someone out there can conjure up a cooler name. Here’s where you come in: you can choose your faves from a list already assembled, or you can submit your own ideas (up to three). The big reveal for the final name will be in May 2014.

This naming contest is part of the 10-year anniversary celebration. The mission will mark a decade of exploring Saturn, its rings and moons on June 30 PDT (July 1 EDT).

The name game is already underway. And they’ve already released an awesome trailer in advance of Cassini’s astounding swan song.

No, really, watch the trailer.

This is going to be so cool.

Cassini’s last mission could well be the inspiration of our next generation of scientists. It really is all that.

The Enceladus Deep

Our love affair with Enceladus grows deeper:

PIA18071A substantial ocean most likely exists beneath the icy surface of Saturn’s diminutive moon Enceladus, raising the possibility that primitive forms of extraterrestrial life exist in its briny depths.

The ocean lies between the moon’s rocky core and a layer of thick ice, and is estimated to be about the size of Lake Superior. That’s large for a moon that is only 310 miles (500 kilometers) in diameter and could fit within the borders of Arizona.

In our solar system, the only other moon known to have similar contact between liquid water and rock is Jupiter’s Europa. Both the rock and the water are considered to be essential for the chemistry that could, over eons, turn nonliving matter into living entities.

“The main implication of our work is that there are potentially habitable environments in our solar system that are entirely unexpected,” said Luciano Iess, an aerospace engineer at the Sapienza University of Rome and lead author on the study published Thursday in the journal Science.

(Kaufman)

The essential question is actually a matter of opinion, sort of: How important is this?

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Postcard From Cassini

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There is always this. Given the times, and the scale of science fiction, perhaps the idea of a holiday snap featuring four moons does not necessarily strike us as anything special. But then we stop to think about it:

Two pairs of moons make a rare joint appearance. The F ring’s shepherd moons, Prometheus and Pandora, appear just inside and outside of the F ring (the thin faint ring furthest from Saturn). Meanwhile, farther from Saturn the co-orbital moons Janus (near the bottom) and Epimetheus (about a third of the way down from the top) also are captured.

Prometheus (53 miles, or 86 kilometers across) and Pandora (50 miles, or 81 kilometers across) sculpt the F ring through their gravitational influences. Janus (111 miles, or 179 kilometers across) and Epimetheus (70 miles, or 113 kilometers across) are famous for their orbital dance, swapping places about every four years. They are also responsible for gravitationally shaping the outer edge of the A ring into seven scallops.

NASA/JPL-Caltech/SSI)

Just to go clockwise, that’s Epimetheus, Prometheus, Pandora, and Janus.

Seriously, though … anyone have a holiday snap to match? Didn’t think so.

Shine On, Cassini

Titan Layers (detail)

“Each flyby gives us a little more knowledge of Titan and its striking similarities to our world. Even with its cold surface temperatures of minus 290 degrees Fahrenheit (94 kelvins), Titan is like early Earth in a deep freeze.”

(Hill)

It’s a cosmic diamond jubilee, of sorts. The clock is running, with Cassini set to undertake it’s T-99 flyby of Titan tomorrow (March 6, 2014; 0725 PST). An additional flyby undertaken after the original schedule was settled makes this officially the spacecraft’s one-hundredth survey of Saturn’s largest moon.

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Adjectives Aside ….

The headline might be overwritten, but what are you going to do?

The classic model of Saturn’s atmosphere portrays it as a layered sandwich of sorts, with a deck of water clouds at the bottom, ammonia hydrosulfide clouds in the middle, and ammonia clouds near the top. Those layers are just below an upper tropospheric haze of unknown composition that obscures almost everything.

Detail of Saturn storm false-color.But this storm appears to have disrupted those neat layers, lofting up water vapor from a lower layer that condensed and froze as it rose. The water ice crystals then appeared to become coated with more volatile materials like ammonium hydrosulfide and ammonia as the temperature decreased with their ascent, the authors said.

“We think this huge thunderstorm is driving these cloud particles upward, sort of like a volcano bringing up material from the depths and making it visible from outside the atmosphere,” said Sromovsky. “The upper haze is so optically thick that it is only in the stormy regions where the haze is penetrated by powerful updrafts that you can see evidence for the ammonia ice and the water ice. Those storm particles have an infrared color signature that is very different from the haze particles in the surrounding atmosphere.”

In understanding the dynamics of this Saturn storm, researchers realized that it worked like the much smaller convective storms on Earth, where air and water vapor are pushed high into the atmosphere, resulting in the towering, billowing clouds of a thunderstorm. The towering clouds in Saturn storms of this type, however, were 10 to 20 times taller and covered a much bigger area. They are also far more violent than an Earth storm, with models predicting vertical winds of more than about 300 mph (500 kilometers per hour) for these rare giant storms.

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So tell me this isn’t embarrassing: I actually took my daughter outside to wave at Cassini last month, praising the almighty coincidences of physics, chemistry, biology, neurology, psychiatry, and psychology that brought me to remember, just in time, that this was happening. The young lady, of course, was less than impressed.

So I didn’t mention anything to her, later, about how I went back down to my desk, after tucking her into bed, congratulating myself and feeling all self-satisfied, and then looking again and realizing that while JPL and I share a time zone, the shoot was planned for that hour UTC.

Damn.

Earth and Moon, as seen from Saturn; July 19, 2013Color and black-and-white images of Earth taken by two NASA interplanetary spacecraft on July 19 show our planet and its moon as bright beacons from millions of miles away in space.

NASA’s Cassini spacecraft captured the color images of Earth and the moon from its perch in the Saturn system nearly 900 million miles (1.5 billion kilometers) away. MESSENGER, the first probe to orbit Mercury, took a black-and-white image from a distance of 61 million miles (98 million kilometers) as part of a campaign to search for natural satellites of the planet.

In the Cassini images Earth and the moon appear as mere dots—Earth a pale blue and the moon a stark white, visible between Saturn’s rings. It was the first time Cassini’s highest-resolution camera captured Earth and its moon as two distinct objects.

It also marked the first time people on Earth had advance notice their planet’s portrait was being taken from interplanetary distances. NASA invited the public to celebrate by finding Saturn in their part of the sky, waving at the ringed planet and sharing pictures over the Internet. More than 20,000 people around the world participated.

“We can’t see individual continents or people in this portrait of Earth, but this pale blue dot is a succinct summary of who we were on July 19,” said Linda Spilker, Cassini project scientist, at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Cassini’s picture reminds us how tiny our home planet is in the vastness of space, and also testifies to the ingenuity of the citizens of this tiny planet to send a robotic spacecraft so far away from home to study Saturn and take a look-back photo of Earth.”

Cassini Dances With Crystals

Cassini, ever faithful, brings out the geek in Matt Hedman. And it is to our great benefit:

Since July 19, when Cassini positioned itself in Saturn’s shadow and began gathering data from this rare vantage point, ring scientists such as myself have been poring over the streams of data coming back. We’re waiting—as you all are—to see the full mosaic of the Saturn system stitched together by the imaging team, but in the mean time, we’ve been looking at individual images and near-infrared data to see what we can learn about Saturn’s rings.

Images of Saturn and its rings backlit by the sun are not only exceptionally beautiful, they also provide us with unique information about Saturn’s rings. Earlier backlit images of Saturn’s rings obtained by Cassini back in 2006 and 2012 revealed previously unseen dusty rings as well as unexpected structures in already known rings. The new mosaic will allow us to look again at some of the hardest-to-see rings, to track changes in the distribution of tiny ice grains near Enceladus’ orbit, and to investigate differences in the particle sizes among different dusty rings.

When Cassini looks back towards the sun during opportunities like these, the rings that are most easily seen from Earth appear fairly dark to Cassini. The reason is that the rings we Earthlings can see through telescopes are mostly formed from pebble-to boulder-sized particles, and they are getting the full blast of illumination from the sun. Cassini, however, is looking at the unlit sides of these objects. By contrast, other rings like the D, E and G rings appear exceptionally bright from Cassini’s vantage point. This occurs because the tiny dust-sized grains in these so-called “dusty rings” are very good at scattering light when the sun is behind them. (Just think of how dust motes floating around in a room become visible when we look towards bright windows.)

PIA08328Since dusty rings are so much easier to see in backlit images, extremely tenuous rings that are otherwise very difficult to detect become clearly visible. In the images Cassini took of the Saturn system in 2006, we can see faint ringlets lying along the orbits of Saturn’s small moons Pallene and Janus. These rings are likely composed of material knocked off the surface of their respective moons by micrometeoroids. We are keen to get another clear look at these features to see if they have changed over the last seven years – which is about the length of a Saturn season. In particular, we are interested in seeing if changes in Janus’ orbit over the last few years due to its interactions with Epimetheus have influenced the structure of its ring.

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Enceladus Unveiled

Enceladus and friendsInertia.

Never mind.

Let us start, then, with something a little more recent, since there is much to see.

Enceladus, perhaps our favorite celestial body in the solar system.

And, ah, Cassini!

The intensity of the jets of water ice and organic particles that shoot out from Saturn’s moon Enceladus depends on the moon’s proximity to the ringed planet, according to data obtained by NASA’s Cassini spacecraft.

The finding adds to evidence that a liquid water reservoir or ocean lurks under the icy surface of the moon. This is the first clear observation the bright plume emanating from Enceladus’ south pole varies predictably. The findings are detailed in a scientific paper in this week’s edition of Nature.

“The jets of Enceladus apparently work like adjustable garden hose nozzles,” said Matt Hedman, the paper’s lead author and a Cassini team scientist based at Cornell University in Ithaca, N.Y. “The nozzles are almost closed when Enceladus is closer to Saturn and are most open when the moon is farthest away. We think this has to do with how Saturn squeezes and releases the moon with its gravity.”

Cassini, which has been orbiting Saturn since 2004, discovered the jets that form the plume in 2005. The water ice and organic particles spray out from several narrow fissures nicknamed “tiger stripes.”

“The way the jets react so responsively to changing stresses on Enceladus suggests they have their origins in a large body of liquid water,” said Christophe Sotin, a co-author and Cassini team member at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Liquid water was key to the development of life on Earth, so these discoveries whet the appetite to know whether life exists everywhere water is present.”

Just a reminder: NASA is an example of a government agency doing its job; that’s why congresses and presidents alike prefer to cut its budget.
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No, really, click that link; it’s important.